I have had .002 neck tension for loads but had them set up expecting bullet set back. For my 556 it was .001ish set back. WIth my 308 AR it was more of set back and caused problems. I ordered K&M custom expanders and that has been titties. You should not need a SB die.
you could easily do all with a 18-22" barrel while keeping it maneuverable. Hell you can run a 16" and hornady superformance ammo and be good. I believe they have 165sst superformance loads too which should run pretty fast. You have a suppressor?